Unexpected stability of CuO/Cryptomelane catalyst under Preferential Oxidation of CO reaction conditions in the presence of CO2 and H2O

Abstract The catalytic activity of CuO/Cryptomelane for the preferential oxidation of CO in H2-rich streams has been studied in the absence and presence of H2O and CO2, paying special attention to the catalyst stability and to changes on its physical-chemical properties under CO-PROX reaction conditions. For fresh CuO/cryptomelane catalyst, the presence of CO2 and/or H2O in the CO-PROX feed partially inhibits CO oxidation due to chemisorption of H2O and CO2 on the catalyst. H2O chemisorption on CuO/Cryptomelane is stronger than CO2 chemisorption, and simultaneous CO2 and H2O adsorption has a synergetic effect that enhances co-adsorption and significantly hinders CO oxidation. On the contrary, the presence of CO2 + H2O in the CO-PROX reaction mixture has a positive effect in the CuO/Cryptomelane stability upon several consecutive reaction cycles in the 25–200 °C range. XRD showed that chemisorbed CO2 + H2O species partially prevent the catalyst deactivation due to cryptomelane reduction to hausmannite (Mn3O4) under the strongly reductive environment of the CO-PROX reaction, and H2-TPR and Raman spectroscopy characterisation support that the cryptomelane structure is less damaged under CO-PROX conditions in the presence of CO2 and H2O than in the absence of these species. Therefore, interestingly under CO2 + H2O environment (realistic CO-PROX conditions) CuO/Cryptomelane catalyst performs an improved catalytic activity.